The invention relates to a method of controlling the threshold of a threshold decoder for a signal having several levels, in which the threshold value of the decoder is programmable. The invention also relates to a television receiver provided with a decoder controlled in accordance with the method.
The invention provides a means for utilizing the possibilities of a threshold decoder when a signal, having several levels, is, perturbed by quasi-stationary echoes. It is thus, typically usable in the case of cable distribution networks, for example, in a MAC standard for optimally controlling each receiver.
The threshold of threshold decoders is usually controlled as a function of the amplitude of the signal without taking into account its behavior in the presence of echoes. In the case of MAC, the control is effected by adapting the threshold with respect to the black/white level in line 624.
The echoes produce directly visible faults in the image and a noise which is referred to as clamping noise and which is extremely troublesome, particularly for long echoes. Echoes degrade the error rate in binary data.
To improve the behavior of decoders in the presence of echoes, it is known to utilize an equalizer. The effectiveness of such arrangements is not disputed, but they are quite costly.